Natural gas hydrates are ice-like solids that form when methane gas and water are exposed to high pressures and low temperatures. Hydrates are formed when hydrogen-bonded water molecules organize into networks that can vary in size depending on the structure of the encapsulated guest molecules. Gas hydrates can be easily formed during the transportation of oil and gas in pipelines when the appropriate conditions are present. If hydrates are not managed properly, they often result in lost oil production, pipeline damage, and safety hazards to field workers.
There are several methods to avoid hydrate blockages. These methods include raising the temperature (e.g., insulation, and electric or water heating), lowering the pressure, removing the water, and adding anti-freeze chemicals. These techniques are often very expensive and difficult to manage. Perhaps the most common method of hydrate inhibition in the oil and gas industry is the addition of thermodynamic inhibitors (anti-freeze chemicals). These substances shift the hydrate formation temperature and therefore reduce the temperature at which the hydrates form at a given pressure and water content. Methanol and ethylene glycol are among the most common thermodynamic inhibitors used in the oil industry. Although thermodynamic inhibitors are quite effective, large doses are required to achieve high concentration in the water phase. Thermodynamic inhibitors are regularly dosed at concentrations as high as 50% based on water content during oil and gas production. Therefore, there is a substantial cost associated with the transportation and storage of large quantities of these solvents.
A more cost-effective alternative is the use of low dosage hydrate inhibitors (LDHIs); as they generally require less that 2% dose to inhibit the nucleation, growth, or agglomeration of gas hydrates. There are two general types of LDHIs, kinetic hydrate inhibitors (KHIs) and anti-agglomerants (AAs). KHIs work by delaying the growth of gas hydrate crystals and as anti-nucleators. AAs allow the hydrates to form, but they prevent them from agglomerating and accumulating into larger masses capable of causing plugs. An AA enables gas hydrates to form, but in the shape of fluid slurry dispersed in the liquid hydrocarbon phase. In general, the water cut should be below 50% otherwise the slurry becomes too viscous to transport. As consequence, significant research effort is being dedicated to develop AAs capable of operating under higher water-cuts, and there still exists a need for improved compounds, compositions and methods for preventing formation of gas hydrate agglomerates in the oil and gas industry.